Electric forming



Nov. 23, 1943. s WESTIN T A 2,335,165

ELECTRIC FORMING Filed Sept. 14, 1942 Sven Westip Axel Wes tzn INVENTORS AT TORNEYI Patented Nov. 23, 1943 ELECTRIC FORMING Sven Westin, West Allis, and Axel Westin, Milwaukee, Wis., assignors to A. 0. Smith Corporation, Milwaukee, Wis., a corporation of New York Application September 14, 1942, Serial No. 458,216

Claims.

This invention relates to electric forming, and constitutes an improvement upon certain embodiments of the invention set forth in the earlier application of the present inventors, Serial No. 376,669, filled January 30, 1941, for Improvement in method of treating metallic bodies, now Patent No. 2,309,561, dated January 26, 1943.

The principal objects of the invention are to provide a longer time for the heating cycle and to effect a more uniform distribution of the heating currents throughout the thickness of the article being formed.

Another object is to prevent injury to the article by scoring from the electrode dies.

According to the invention these and other objects are attained by shaping the die surfaces of the electrode segments so that contact is made with the article principally along a longitudinal portion of the surface to the rear of the leading edge of each segment. In this way the current is compelled to flow for a longer distance through the article than would be the case where the edges of the dies made contact for conducting current to the article. This longer path for the current provides a longer heating cycle for each portion of the article during each revolution and also effects a greater penetration of the current where articles of substantial thickness are being formed.

Since the leading edges of the die do not contact the article there is less tendency of scoring the latter.

The invention has been embodied in apparatus for forming a nose on the end of tubular blanks as in the manufacture of bomb shells. Such embodiment is illustrated in the accompanying drawing, in which:

Figure 1 is a longitudinal section through the forming apparatus with the electrical connections shown diagrammatically and showing the blank partially formed; and

Fig. 2 is a transverse section through the electrode dies and blank taken on line 22 of Fig. 1.

The apparatus comprises in general the blank supporting mechanism l and the blank heating and forming mechanism 2.

The blank supporting mechanism 1 comprises an upright support 3 slidably mounted on a base 4 for movement toward and away from the mechanism 2. The support 3 carries a rotary gripping chuck 5 for gripping the end of a tubular blank 6 to be formed and pushing the latter longitudinally on a horizontal axis into the forming dies of the mechanism 2. An electric motor I, or other suitable power means is provided to effect rotation of the chuck 5 and blank 6. The same or a different motor may be employed to effect the longitudinal movement of the blank 6 into the dies.

The blank heating and forming mechanism 2 comprises an upright support 8 mounted on base 4 and holding a pair of electrode die segments 8 and Ill. The segments 9 and ID are constructed of blocks of metal having their ad jacent faces cut out to provide a generally circular die cavity for receiving the end of the blank 6 to be formed, the cavity being of gradually smaller diameter at its rear to give to the blank the desired nose shape as the blank is pushed into it.

The segments 9 and ID are separated either by insulation II or by an air gap, and are connected by leads l2 to a transformer l3 for supplying heating current to the blank from a suitable power line l4. Where more than two electrode die segments are employed, as set forth in the application of Warren F. Heineman, Serial No. 391,234, filed May 1, 1941, now Patent No.

2,313,068, dated March 9, 1943, the leads and transformers may be arranged differently to enable the use of three-phase current.

In carrying out the present invention, the die cavity is constructed with a major and minor axis, the latter being perpendicular to the plane of the insulation ii. A simple way to provide a die cavity of this shape is to first separate the segments 9 and I0 a little farther than the separation provided by the insulation H, and then bore the faces of the segments on a circle, after which the segments are brought against insulation I! and secured in final position.

A few thousandths of an inch difference between the major and minor axis in any transverse plane is suflicient. Too great a difference tends to needlessly work the metal of the blank and may result in an inadequate support for it as it turns in the die.

The major contact between the blank and each die segment will be at the extremes of the minor axis, which is in the central longitudinal portion of each segment. The heating current passing into and out of the blank at the points of major contact on opposite sides of the blank passthrough nearly half the circumference of the blank and provides for a longer heating cycle for each portion of the blank than would be the case if the path of the current in the blank was restricted to the thickness of the insulation ll. Furthermore, there is a greater tendency for the current, in taking a longer path, to penetrate for the full thickness of the blank and thereby heat the latter more uniformly and without undue melting at the surface of the blank.

From one viewpoint the invention may be regarded' as providing difierent contact pressures in difierent circumferential portions of the blank as the latter rotates in the dies, the region of highest pressure being along the longitudinal center line of the face of each electrode die segment, and the region of lowest pressure being at the edges of each, segment. This contact pressure at the edges of the segments is sufiiciently low to force the heating current to pass into the blank in the region of higher contact pressure more remote from the edges of the segments. The aprality of spaced die members constituting complementary segments encircling a die cavity for receiving and forming a relatively rotating article of circular cross section, the die faces of the respective segments having their leading edges as determined by the direction of rotation of the article thereagainst recessed radially outwardly.

2. In apparatus of the class described, a plurality of spaced die members constituting complementary segments encircling a die cavity for receiving and forming a relatively rotating article of circular cross section, the die faces of the respective segments having their leading and trailing edges as determined by the direction of rotation of the article therein gradually recessed radially outwardly.

3. In electric forming apparatus, a plurality of spaced electrode die members constituting complementary segments encircling a die cavity for receiving and forming a relatively rotating article of circular cross section, the die cavity having a major axis and a minor axis at right angles to each other in the transverse plane, the major axis lying in the axial plane extending between the segments.

, 4. In electric forming apparatus, a plurality of spaced electrode die members constituting complementary segments encircling a die cavity for receiving and forming a relatively rotating article of circular cross section, the die face of each respective segment providing a longitudinal re gion of maximum contact pressure with the article bordered by similar regions of relatively low contact pressure.

5. In apparatus for forming metal articles, a die having a substantially circular-confining die cavity for receiving the end of a work piece to be formed by relatively rotary movement between the die and work piece, and a relief in the die cavity in the side thereof to provide for working of the metal as the article is being formed.

SVEN WESTIN. AXEL WESTIN. 

